Re: [photo-3d] Digest Number 328

["John A. Rupkalvis" <stereoscope@xxxxxxxxxxxxx>]

24 frames per second is the standard frame rate for sound film (16mm, 35mm,
and 70mm) in the United States and some other parts of the world, even
though it is 25 frames per second in Europe to correspond to television
frame rates.

Regarding Pulfrich, the amount of parallax perceived is a result of a
combination of the amount of perceivable density difference per unit of
time.  Frame rate is one very convenient method for measuring time, since
you can actually measure the amount of lateral displacement from one frame
to the next.

Also, there very definitely is a stereo base in Pulfrich, although you may
not be aware of it at the time of image acquisition.  The distance the
camera travels laterally in a dolly shot from the point the image is
perceived by one eye to the point the image is perceived by the other eye
determines the stereo base.

Speed and distance are factors, and these can be measured in terms of
differential parallax on the film, since you can calculate how fast the
camera would have had to be moving to yield a specific parallax from one
frame to the next (or any number of frames) at a specific distance for a
known focal length lens.

There is even a stereo base if the camera is standing still and the subject
is moving, although in this case it is relative and only applies to moving
parts of the image.  Again, it can be measured and calculated.

JR

----- Original Message -----
From: "Olivier Cahen" <o_cahen@xxxxxxxxxxxxxxxx>
To: <photo-3d@xxxxxxxxxxx>
Sent: Tuesday, October 31, 2000 12:34 AM
Subject: Re: [photo-3d] Digest Number 328


> Your question, as it is now quoted, has no meaning. The Pulfrich effect
> has nothing common to the frame frequency. There is no frame frequency
> of 24 fps, it is 25 in Europe and 30 in the USA. There is no "stereo
> base" in Pulfrich effect.
> One eye, the one with a darker filter, sees its image later than the
> other eye. The time difference can be about two milliseconds if the
> filter absorbs half of the light intensity. If the filter is on the left
> eye, every object moving from left to right would be seen more to the
> right by the left eye, this means that it would be seen closer than the
> screen. If it moves to the left, it would be seen beyond the screen. All
> the contrary if the darker filter is on the right eye. The colors of the
> filter has no effect. A filter as simple as one polarising glass suited
> for stereo projection is efficient enough.
> You do not need a TV program to experiment Pulfrich effect. Hang any
> object to a thraed and make it swing at the end of its thread. With a
> filter on one eye, you will see it moving along a circle instead of a
> line. Have a look to the street from your window and put a filter on
> your left eye. Look at cars moving to the right, you will see them
> flying over the street.
>
>
> >    Date: Sun, 29 Oct 2000 00:22:03 +0200
> >    From: "Sergio Baldissara" <winter@xxxxxxxxxx>
> > Subject: Re: Re: pulfrich "stereo base"
> >
> > I must thank everybody answered my posting, but I now realize I asked
the
> > wrong question.
> > I had to ask: "what's the time lapse (frame lapse at 24 fps)  between
the 2
> > frames of each stereo pair in Pulfrich movies?"
> > The "stereo base" of course depends upon the panning speed, but I must
know
> > the above figures (in milliseconds or in frames) to set up my panning
speed.
> > Sergio
>
>
>
>